But where's the SDK for iOS 7?

Apple sold approximately 38 million iPhones in the first quarter, an 8% increase over what it sold in the same quarter a year ago, an analyst said today.

Brian Marshall of the ISI Group said today he was sticking with his estimate of 38 million iPhones for the January-March quarter.

Others, including Brian White of Topeka Capital Markets and Gene Munster of Piper Jaffray, have placed their bets on lower numbers -- 35 million and 35.5 million, respectively -- for the quarter that ended March 31, flat or just 1% above last year's number.

The experts, however, are looking ahead more than they're revising recent history.

Marshall, for example, predicted that Apple will release its next iPhone -- which many have been tagging as the "iPhone 5S" in a nod to previous Apple naming conventions -- in late June or early July. White has the same timetable in mind.

That would be a departure from the last two iterations of the smartphone -- the iPhone 4S and iPhone 5 -- which went on sale in October 2011 and September 2012, respectively.

But the return of an iPhone launch to summer, a schedule last used in 2010 for the iPhone 4, faces at least one obstacle: Apple has not yet released a preview of its next iOS SDK (software development kit) to app makers.

In the two most-recent years when Apple has launched a new iPhone in June, it seeded developers with a new SDK several months in advance.

The first beta of the iOS 3 SDK, for example, was released March 17, 2009, 13 weeks before the retail debut of the iPhone 3GS. A preview of the iOS 4 SDK, meanwhile, reached developers April 8, 2010, or 11 weeks before the iPhone 4 went on sale.

If Apple plans to give developers the same amount of time to prep for iOS 7's changes, the iPhone 3GS and iPhone 4 timetables would point to an iPhone 5S on-sales date somewhere between July 4 and July 18, assuming the SDK appeared today.

More recent iOS SDK-iPhone timetables hint at an even later launch of the next iPhone, since the interval between the iOS 5 SDK and the iPhone 4S was 18 weeks, and that between the iOS 6 SDK and the iPhone 5 was 14 weeks. Those schedules suggest an iPhone 5S on-sales launch between July 25 (14 weeks from today) and Aug. 22 (18 weeks).

Either Apple will, best case, ship the next iPhone at the end of the analysts' estimates -- early July -- or the company will give developers less time to craft, or recraft, apps for iOS 7. The second could be trouble.

Marshall had no explanation for the missing SDK other than to note that iOS development was once headed by Scott Forstall, but with his departure last October, the reins were handed to Craig Federighi, who already led OS X development.

Jony Ive, formerly head of industrial design, was also put in charge of what Apple calls "Human Interface," the user interface (UI) and user experience (UX) of its software.

Marshall speculated that the 2012 management overhaul, and Ive's new responsibilities, may have slowed down iOS development.